Burst separating apparatus



Sept. 20, 1960 G. E. KELLY 2,953,636

BURSTV SEPARATING APPARATUS original Filed March 1e, 1953 United StatesPatent O BURST'SEPARATWG APPARATUS Gersen E. Keny, Haddonneld, NJ.,assigner u Radio Corporationof America, a corporation of DelawareOriginal application Mr. 18,-- 1953,v` Ser.N o. 343,060. DividedV and'this application `luly 11,y 1958,' Ser. No. 748,041v k 5 Claims. (Cl.178-5.4)

Thisinventionr relates to color television receiving apparams-and hasparticular reference to apparatusitherein f or separating or recoveringcolor synchronizing bursts from rece'ived composite signals.

This application is a division-of my copending applicationgS'erf` No;343,060, tiled March 18, 1953,l andl entitled (olor Television'Receiving Apparatus.

In tlie type of color television system` whichV is'in' accordanceI withstandards proposed by the National 'Delevision Systems Committee'(NTSC), the side bands of a subcarier wave, which is bothphase-v andamplitude modulatedinl accordance with the color information ofa-subject, areJ interspersed' withr the videol signals representingbrightness of the subject; By properly choosing the equency of the'color subcarrier wave; the color signal modulated' sidey band energycomponents may bemade to fall' between1 the f brightness' signal energykcomponents.

Infsuch systems,l the color' information is-derivedfat a receivc bysynchronouslydemodulating the color subcarrierY vv'ave.` Suchdemodulation' i's clfected under' the control of a reference frequencyoscillator operatingl in suitable frequency and phase synchronism.`

For thefsynchronization'of the receiver color subcarrie'r wave referencefrequency oscillator, it is the present practice'to transmit acompos'itesignalwhich includes, in addition tothe yVideo signalscomprisingbrightness 'and color information, the usual horizontal andvertical synchronizing signals and also bursts of several cycles each ofthe color subcarrier wave frequency respectively following thehorizontal synchronizing signals. Sucha color synchronizing system isdescribed in apublication titled-Recent Developments invv ColorSynchronizationin the RCA Color Television System issued by the RadioCorporation' of America, February 1950. Such a systeml alsoy isdescribed in-U.S. Patent 2,594,380,`v issuedf April 29, 1952 to L. E.Barton and P. 4I-I. Werenfels and titled synchronizing Apparatus forColor Signal Sampling oscillators. The general burst type of colorsynchronizing system also forms the-subject matter of `a copending U.S.patent applic'ation'- of A.- V. Bedford; Serial No'. 143,800, tiledFebruaryv 11j, 1950, andV tigtledfsynchronizing Apparatusvg, now U.S;Patent No; 2,728,812, issued December 27, 1955.

At a receiver operating in Iaccordance with the burst type of colorsynchronizing system, it is necessary to sepatte or recover the' burstof color subcarier" wave fre"- queiicy transmitted in thecornpositesignal'.

An object of the present invention is toprovide'animproved 'apparatusfor separating the bursts ofcolor subcarrier Wave' from a compositetelevision signal andlvvhich provides a higher degree of noise immunitythan apparatus heretoforefemployed.

In accordance with the invention, acolor television receiver includes aburst signal separator electron tube uponV the g'rid circuit of Which= acomposite signal, including burstsof the color subcarrier wave, isimpressed. The tube is normally unresponsiveV to" the compositesignalangl is periodically rendered conducting during substantially Vdeilection apparatus with thatofthetransmitter.

only the reception period of the subcarrier wave frequency bursts toproduce in' its anode circuit the' subcarrier wave frequency burstsexclusively of the rest of the composite signal.'4 A feature of a burstsignal separator apparatus in accordance with the present invention isits relatively highl immunity to noise. The composite signal'isimpressed upon the grid circuitof the" burst separator tube by means ofVa resonant-circuit' which is tuned to the subcarrier Wave frequency.The burst separator tube is rendered operative' momentarily by meansv ofkeying pulses controlled by horizontal synchronizing signals; Bysuchmeans-,f the subcarrier wave frequency bursts are products in theanode circuit ofthe burst separator tube exclusively ofthe rest of the'composite signal and also substantially exclusively of random'noise. l

The novel features thfat'ffa'ie'considered-characteristic of thisinvention are set forth with particularity in ther ap# pended claims.-Theiinvention itself, however, both as tov its organization and methodof operation, as well as additional objects and advantages thereof,-will best be understood from the following description when read inconnectionfwith the accompanyingdrawing.

The single ilgure'of the drawing is a circuit diagram, partly in blockform, ofv an color televisiony receiver synchronizing system includingburst separator apparatus in' accordance Witlrthe'present invention;

With reference" n'o'w to the'drawing, the illustrative embodimentof theinvention will be' described. This description will notV include'reference'to circuit details, which may bereadily' seenfrom the drawing.The'value's of` theiessential components areindicated' and are inaccordance"- substantially witha practicalv embodiment ot the inventionwhich has successfully operated.y In indicating these values, allresistance-values :are in-ohm, all capacitance values lessV thanare'in-miciofarads and greater than l-.0v are' inmicromicrofa'rads,unless otherwise" noted; Also infa conventional manner,r K, used inthevvalues of some'of' ther'esistors", equals l-OOOy ohms;

ItA Will'- be assumedl that there" is inip'ressedupony input terminal-1- acomposite television signal derived froml the secondf detector, forexample; of a superheterodyne'- receiver: This composite televisionsignal Willv beV` understoodt'o includeafvideo signall componentincluding'- both .brightness informationi andi color information of fasubject in the form of a'phase and amplitude'modulated subca-rn'erWavefhaving alnominalfrequency equal substantially to one of the higherbrightness component frequencies. The coin'p'osite signal also will beunderstood` to include the usual horizontal andV vertical' synchronizingsignals ttor-maintaining synchronous operation of the receiver Inaddition, the'compositefsi-gnal also will be'unclerstoodtoinclude albursty ofl several cycles* of the colo-r subcarricr wave frequencysuperimposed substantially on theback porch of the horizontalsynchronizing signals.

The composite television signal appearing at the terininall V` isimpressed upon the grid circuit of a first video amplitiestageiincluding-anfelectnon tube 2'. The cathode circuit of this tube'isl connected to apparatus including af contrast centrer potentiometersvwhichf is coupledin a that it is no part of the present invention `andis not necessary to an understanding of the invention.

The anode circuit of the composite signal amplifier 2 is coupled to async signal separator 6 for the separation from the composite signal ofthe horizontal and vertical synchronizing signals in -a conventionalmanner. The horizontal synchronizing signals are impressed upon ahorizontal automatic frequency control (AFC) apparatus 7 which will beunderstood to include a horizontal deection oscillator which ismaintained in synchronous oper-ation with the received horizontal syncsignals in the usual manner. The output of the horizontal AFC apparatus7 is coupled to` `a horizontal deflection output circuit 8 which may, asusual, include a power amplier stage, the output of which is coupled tothe primary winding 9 of a horizontal deflection output transformer 10.The primary winding 9 of the horizontal deflection output transformermay be coupled to the horizontal deflection yoke winding and to a highvoltage rectifier circuit substantially as indicated in a conventionalmanner. The transformer 10 also has a secondary winding 11 in which todevelop keying pulses in response to horizontal retrace or flyback. Theuse of these keying pulses will be described subsequently.

The anode circuit of the first video amplifier tube 2 includes acoupling transformer having a primary winding 12 and a secondary winding13. These two windings are tightly coupled. The secondary winding isconnected to the control grid circuit of a burst separator electron tube14. The winding 13 is tuned by means of the input circuit capacitanceofthe tube 14 and distributed capacitance for resonance substantially atthe subcarrier wave frequency. By such means, the input grid circuit ofthe burst separator tube is prevented from charging up on synchronizingsignal information having -a narrow pass band of approximately .5 mc.band width centering about the subcarrier wave frequency.

The anode circuit of the burst separator tube 14 includes a bi-lar burstsignal output coupling transformer 15, the primary winding 16 of whichis connected as part of the yload circuit -for the burst separator tubeand the secondary winding 17 of which is tapped at an intermediate pointwhich is effectively grounded, as indicated. The secondary winding 17 ofthe burst output transformer is coupled to the `double diode phasedetector electron tube 18. By means of the described secondary winding17 of the coupling transformer 15, the phase detector is driven in apush-pull manner which cancels any undesirable second harmonics whichmay be developed due to clipping of the separated burst of subcarrierwave frequency.

The output circuit of the phase detector which is deiived from abalancing potentiometer 19 is coupled to the input grid circuit of areactance tube 21 so as to control the operation of the reactance tubein accordance with any detected phase deviations. The anode circuit ofthe reactance tube includes a parallel resonant circuit 22 which istuned at a frequency which is somewhat lower than the frequency of thecolor subcarrier wave.

The apparatus also includes an oscillator tube 2.3 which is operated `asa cathode follower having a parallel resonant circuit 24 connected aspart of its cathode circuit and tuned -at a frequency which is lowerthan the subcarrier wave frequency. Preferably, the frequency at whichthe cathode tuned circuit 24 is resonant is between the frequency of thecolor subcarrier wave and the frequency at which the resonant circuit 22in the reactance tube anode circuit is tuned. The grid circuit of theoscillator tube 23 `alsof is tuned by means including a piezo-electriccrystal 25. The tuning of this circuit is substantially to the frequencyof the color subcarrier wave. The anode circuit of the reactance tube 21is coupled to the grid circuit of the oscillator tube 23 so as tocontrol the frequency of the oscillator in accordance with the operativecondition of the reactance tube.

-tube 21 in a conventional manner.

The subcarrier wave frequency is `derived from the oscillator tube fromthe cathode circuit which, as indicated, is connected to the doublediode 18 of the phase detector. The variable capacitor 26 is employed toneutralize any coupling between the burst output transformer 15 and thecoil 27 of the oscillator cathode tuned circuit 24. The capacitor 26performs the desired neutralization by equalizing the shunt capacitancesof the diode 18. Any coupling between the burst transformer 15 and theoscillator coil 27 appears `as an error voltage in the output circuit ofthe phase detector when weak signals are encountered, thereby tending toreduce the operative effectiveness of the AFC system.

The output of the oscillator 23 also is impressed upon the synchronousdemodulator 5 by means of a coil or winding 2S coupled to the oscillatorcoil 27 and together with which to comprise a subcarrier wave outputtrans.

former 29. It will be understood that the arrangement of the subcarrierwave output transformer relative to the synchronous `demodulatoi 5 isentirely diagrammatic and is not intended to indicate the details ofsuch a coupling. In accordance with the conventional practice in theoperation of receivers of this type, different phases of the referencewave are impressed upon different sections of the synchronousdemodulator for the purpose of separately deriving the ldifferent colorrepresentative signals. Details of this character form no part of thepresent invenltion and are not required for an understanding thereof andaccordingly are omitted in the interest of clarity.

In the operation of the described apparatus embodying an automaticfrequency control system in accordance with the invention, `a compositetelevision signal 31 is im pressed upon the control grid circuit of theburst separator tube 14. This composite signal includes a videocomponent 32, a horizontal synchronizing signal 33 and a burst signal 34of several cycles of a color subcarrier wave superimposed substantiallyon the back porch of the horizontal synchronizing signal. Keying pulses35 of negative polarity derived from the secondary winding 11 on thehorizontal deection output transformer 10 are impressed upon the cathodecircuit of the burst separator tube 14 in suitable time relationship tothe composite signal 31 to render the tube 14 operative substantiallyonly during the interval that the burst signal 34 is impressed upon thegrid circuit of the tube. Accordingly, the separated burst signal 36 isdeveloped in the anode circuit of the burst separator tube 14. lt willbe understood that the burst signal 36, as well as the received burstsignal 34, is of substantially sinusoidal wave form. Also, it will beunderstood that the subcarrier reference frequency wave produced by theoscillator tube 23 is of substantially sinusoidal form.

Deviations in the phase of the separated burst signal 36 and thesubcarrier reference frequency wave produced by the oscillator tube 23and detected by the apparatus including the double diode 18 producessubstantially unidirectional voltages in the output potentiometer 19varying in polarity in accordance with the sense of the phase deviationand in amplitude in accordance with the magnitude of the phasedeviation. These substantially unidirectional voltages control theoperation of the reactance The reactance tube, in turn, controls thefrequency of the oscillator including the tube 23 so as to make itconform with the frequency and phase of the received subcarrier waveyfrequency burst signal 34.

The improved type of burst signal separator in accordance with thisinvention has the advantage of maintaining substantially uniformamplitude of the separated bursts regardless of noise conditionsencountered. Furthermore, the keying of the cathode circuit of the burstsignal separator by means of a negative pulse derived from thehorizontal deecton output circuit prevents the grid of the burst signalseparator tube from charging asis-3,636

up on noise pulses at times other than those in which the burst signalis received.

The described coupling between the first video, or cornposite signal,amplifier and the burst signal separator tube, including the tightlycoupled transformer coils 12 and 13, the secondary of. which is tunedlwith the input capacitance of the burst separator tube has the advantageof eliminating the charging up of the burst signal separator gridcircuit on any synchronizing signal information having frequencies lyingwithin a narrow pass band centered around the color subcarrier wavefrequency. Another advantage ofthis type of burst signal separatorderived from the use of the bi-filar transformer having a tappedsecondary winding and1 coupling the burst signal separator to the phasedetector is that it makes it possible to drive the phase detector in apush-pull manner. The push-pull` type of. operation cancels anyundesired second harmonics Ywhich may be developed due to a clippingaction performed by theV burst separator tube.

Thenature of the invention having been indicated in a description of anillustrative embodiment thereof, its scope is pointed out in theappended claims.

I claim:

1. In a color television system in which a received composite signalincludes, in addition to video signals, horizontal synchronizing signals-to maintain synchronous operation of a receivers horizontal defiectionapparatus and also bursts of several cycles each of a color subcarrierWave frequency respectively following said horizontal synchronizingsignals to maintain synchronous operation of a receivers synchronouscolor subcarrier wave demodulating apparatus, a system for separatingsaid frequency bursts from said composite signal comprising, a compositesignal amplifier stage including an electron tube having cathode, gridand anode circuits, a burst separator electron tube having cathode, gridand anode circuits, horizontal synchronizing signal separator apparatus,a horizontal deflection output circuit coupled for its control to saidsynchronizing signal separator apparatus, means impressing said receivedcomposite signal upon said composite signal amplifier tube grid circuit,means coupling said amplifier tube anode circuit to said synchronizingsignal separator apparatus, said signal amplifier tube cathode circuitserving as an output circuit for said video signals, means including aresonant circuit tuned to said subcarrier wave frequency coupling saidsignal amplifier -tube anode circuit to said burst separator tube gridcircuit, means biasing said burst separator tube to be unresponsive tosaid composite signal impressed upon its grid circuit, and meanscoupling said horizontal deflection output circuit to said burstseparator tube cathode circuit to impress keying pulses upon said burstseparator tube to render it momentarily operative to produce in itsanode circuit said subcarrier wave frequency bursts exclusively of therest of said composite signal.

2. In a color television system in which a received composite signalincludes, in addition to video signals, horizontal synchronizing signalsto maintain synchronous operation of a receivers horizontal deflectionapparatus and also bursts of several cycles each of a color subcarrierwave frequency respectively following said horizontal synchronizingsignals to maintain synchronous operation of a receivers synchronouscolor subcarrier wave demodulating apparatus, a system for separatingsaid frequency bursts from said composite signal comprising, a compositesignal amplifier stage including an electron tube having cathode, gridand anode circuits, a burst separator electron tube having cathode, gridand anode circuits, horizontal synchronizing signal separator apparatus,a horizontal deflection output circuit including a transformer having aprimary and a secondary winding, means `coupling said primarytransformer winding to said synchronizing signal separator apparatus tocontrol the operation of said horizontal deflection output circuit,means impressing said received composite signal upon said' compositesignalf amplifier tube grid circuit,

means coupling said) amplier` tube anode circuit to said synchronizingsignal separator apparatus said signal amplifier tube cathode circuitserving as an output circuit for said video signals, means including aresonant circuit tuned to said subcarrier wave frequency coupling saidsignal amplifier'tube anode circuit to said burst separator tube gridcircuit, means biasing said burst separator tube to be unresponsive tosaid composite signal impressed upon its grid circuit, and meanscoupling said secondary transformer winding to said burst separator tubecathode circuit to impress keying pulses upon said lburst separator tubeto render it momentarily operative to produce in its anode circuit saidsubcarrier wave frequency bursts exclusively of the rest of saidcomposite signal.

3. In a color television system in which a received composite signalincludes, in addition to video signals, horizontal synchronizing signalsto maintain synchronous operation of a receivers horizontal deflectionkapparatus and also bursts of several cycles each of a color subcarrierwave frequency respectively following said horizontal synchronizingsignals to maintain synchronous operation of a receivers synchronouscolor subcarrier wave demodulating apparatus, a system for separatingsaid frequency bursts from said composite signal comprising, a compositesignal amplifier stage including an electron tube having cathode, gridand anode circuits, a burst separator electron tube having cathode, gridand anode circuits, horizontal synchronizing signal separator apparatus,a horizontal deflection output circuit coupled for its control to saidsynchronizing signal separator apparatus, means impressing said receivedcomposite signal upon said composite signal amplifier tube grid circuit,means coupling said amplifier tube anode circuit to said synchronizingsignal separator apparatus, said signal amplifier tube cathode circuitserving as an output circuit for said video signals, means including aresonant circuit comprising a coil coupled to said signal amplifier tubeanode circuit and to said burst separator tube grid circuit, said coilbeing tuned with said burst separator tube grid circuit capacitance tosaid subcarrier wave frequency, means biasing said burst separator tubeto be unresponsive to said composite signal impressed upon its gridcircuit, and means coupling said horizontal deiiection output circuit tosaid burst separator tube cathode circuit to impress keying pulses uponsaid burst separator tube to render it momentarily operative to producein its anode circuit said subcarrier wave frequency bursts exclusivelyof the rest of said composite signal.

4. In a color television system in which a received composite signalincludes, in addition to video signals, horizontal synchronizing signalsto maintain synchronous operation of a receivers horizontal deiiectionapparatus and also bursts of several cycles each of a color subcarrierwave frequency respectively following said horizontal synchronizingsignals to maintain synchronous operation of a receivers synchronouscolor subcarrier wave demodulating apparatus, a system for separatingsaid frequency bursts from said composite signal comprising, a compositesignal amplifier stage including an electron tube having cathode, gridand 4anode circuits, a burst separator electron tube having cathode,grid and anode circuits, horizontal synchronizing signal separatorapparatus, a horizontal deflection output circuit coupled for itscontrol to said synchronizing signal separator apparatus, meansimpressing said received composite signal upon said composite signalamplifier tube grid circuit, means coupling said amplifier tube anodecircuit to said synchronizing signal separator apparatus, said signalamplifier tube cathode circuit serving as an output circuit for saidvideo signals, a transformer having a primary winding coupled to saidamplifier tube anode circuit and a secondary winding coupled to saidburst separator tube grid circuit, said secondary winding being tightlycoupled to said primary winding and tuned with said burst separator tubegrid circuit capacitance to said subcarrier wave frequency, meansbiasing said burst separator tube to be unresponsive to said compositesignal impressed upon its grid circuit, and means coupling saidhorizontal deiection ouptut circuit to said burst separator tube cathodecircuit to impress keying pulses upon said burst separator tube torender it momentarily operative to produce in its anode circuit saidsubcarrier wave frequency bursts exclusively of the rest of saidcomposite signal.

5. In a color television system in which a received composite colortelevision signal includes, in addition to a color subcarrier wavemodulated in accordance with color' information, periodically recurringsynchronizing bursts of the color subcarrier Wave frequency formaintaining synchronous operation of a receivers synchronous colorsubcarrier wave demodulating apparatus, the combination comprising, acomposite signal amplier stage including an electron tube havingcathode, control grid and anode circuits, a burst separator electrontube having a cathode, control grid and anode, means for applying saidreceived composite signal to said composite signal amplifier tube gridcircuit, means for coupling said color subcarrier wave demodulatingapparatus to said composite signal amplifier tube cathode circuit, meansincluding a resonant circuit tuned to said subcarrier Wave frequency forcoupling said burst separator tube grid to said cornposite signalamplier tube anode circuit, means for biasing said burst separator tubeto be normally unresponsive to signals applied to its grid from saidcomposite signal amplier tube anode circuit, a source of keying pulseswhich occur in substantial coincidence with said recurring bursts, andmeans for applying said keying pulses to said burst separator tubecathode in such polarity as to` oppose the bias provided by said biasingmeans and to render said burst separator tube operative to produce atits anode said subcarrier Wave frequency bursts to the exclusion of theportions of said composite signal intervening said recurring bursts.

References Cited in the file of this patent Admiral 38A ExperimentalChassis Circuit, from Admiral Introduction to Color Television, February1954.

RCA Model 21-CT-55 Circuit, November 1954.

